David LeMaster has developed mutants of E. coli that allow for labeling of proteins in alternate carbons. These organism are cultured on glycerol labeled either at C2 or C I and C3. Proteins expressed in this background are labeled at alternate carbons and are used to stud side chains motion by NMR relaxation methods. The alternate labeling is key to the success of this approach, because the complications that arise from 13C_ "C dipolar interactions present in uniformly labeled proteins have been eliminated. SIR has incorporated deuterium specifically into 1,3- 13 C2- and 2-"C-labeled glycerol which will result in more isolated 13C_ 'H vectors for which dynamics will be interpretable.